Implement the version control provenance mapping algorithm

[ghost]

The SDK should have a help method that implements the algorithm described in oasis-tcs/sarif-spec#248, "Version control details not strongly associated result", which introduced the property versionControlDetails.mappedTo of type fileLocation.

Since a result can have more than one location, IMO the input to the algorithm should be a FileLocation rather than a Result . We can either implement it in the FileLocation partial class or as an extension method on FileLocation. Since this functionality isn't core to the notion of fileLocation, it feels more like an extension method to me:

public static VersionControlDetails GetRepositoryForFile(
    this FileLocation fileLocation,
    VersionControlDetails[] versionControlProvenance);

@michaelcfanning FYI